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Because I use a metal detector a lot,(and have a lot of fun doing it!), I own a "White" brand detector that probably cost a lot more than you wish to spend. However, because metal detectors vary so much in what they can "do" and what they are able to "find", the price you'll pay all depends on how serious you may wish to find, interesting and even valuable items.
Some metal detectors can tell you, (within a fairly good percentage of accuracy), exactly what it is you're looking at and at a depth of many inches below ground. Others, are going to "beep", every time you run one over a buried rock in the ground.
You can purchase a fairly decent and accurate metal detector for around $100.00, that should be plenty accurate enough for use on your "occasional camping trips".
The only "features" I would really look for, for one in this price range, would be its ability to tell you approx.what it is you're looking at under several inches of dirt, and not simply "go off", because it has encountered "something solid".
Be careful though! "Metal detecting" can EASILY become very addictive and lots of fun, so you might consider starting out with a fairly decent quality machine, right from the get-go.
A fairly inexpensive detector is the "Bounty Hunter EX", which sells on line for around $100.00.
Anything less than one in this price range, you may spend a lot more in replacing batteries constantly, than had you purchased a decent detector to begin with.

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